Technical Field
The present invention relates to a technical field of membrane, and more particularly to a hydrophobic-oleophilic hollow fiber composite membrane and a preparation method thereof.
Description of Related Arts
With the development of society and industrialization advancement speeding up, the water environment pollution caused by the direct discharge of oily wastewater has become increasingly serious, threatening human health and safety seriously. In recent years, membrane separation technologies have been widely applied in various water treatment fields. In wastewater treatment, membrane separation technology has a promising prospect of application for its features, including high separation efficiency, high purity of separated products and low operation cost, Therefore, in the process of wastewater treatment, it will be of great importance for directly selective separation and recycling of oil products using the high selectivity of membrane separation technology.
Among various oily treatment methods, using oil adsorbents is the common one. In view of the defects of traditional oil adsorbents, such as low oil absorption, poor oil-water selectivity and poor oil preservation after oil absorption, researchers have researched and developed oil absorption resin and related products. Ayman M. Atta et al. successfully prepared granular high-oil-absorption resin by using ethylene glycol dimethacrylate (EGDMA) as a cross-linking agent (Journal of Applied Polymer Science, 2005, Volume 97, Page 80-91). A patent CN1884322A discloses a preparation method for a recyclable acrylics high-oil-absorption material. Xiao Ma et al. prepared a kind of methacrylate absorptive functional fiber with three-dimensional cross-linked network structure using a reactive extrusion and melt spinning method (Journal of Functional Materials, 2013, Issue 2, Page 177-181, Research on property of absorptive functional fiber based on polymethacrylate prepared via reactive extrusion and melt-spinning). Although the traditional oil adsorbents can achieve the purpose of oil-water separation, they have obvious defects, for example, these oil adsorbents are required to be replaced or regenerated after reaching saturated absorption for next adsorption. It not only lowers service efficiency and enhances treatment cost, but also can't meet the demands of continuous, quick and efficient treatment of oily wastewater.
Graphene is a kind of novel two-dimensional carbon material with large specific area, high hydrophobicity, etc. By exploiting these characters, researchers have developed various graphene-based oil adsorbents. D Zha et al. prepared a super-hydrophobic and oleophilic PVDF/graphene porous material by using a diffusion and freeze-drying method (Carbon, 2011, Volume 49, Page 5,166-5,172, Super-hydrophobic polyvinylidene fluoride/graphene porous material). D D Nguyen et al. prepared graphene-based sponge with high adsorption capacity and oil-water selectivity by a dip-coating method (Energy & Environmental Science, 2012, Volume 5, Page 7,908-7,912, Preparation of super-hydrophobic and super-oleophilic graphene-based sponge by simple dip-coating). Z Niu et al. prepared reduced graphene oxide foams by using a method similar to “fermentation”, and its maximum absorption capacity of engine oil can reach 37 times the weight of itself (Advanced Materials, 2012, Volume 24, Page 4,144-4,150, Preparation of redox graphene-based foam by fermentation). Though the graphene-based oil adsorbents have remarkable oil absorption capacity, they work intermittently, still cannot meet the demands of continuous and efficient oil-water separation, limiting its promotion and application.
The membrane separation technology with high separation efficiency, low energy consumption and small area occupied, and has a huge development potential in the treatment of oily wastewater. At present, hydrophilic-oleophobic membranes are usually used for the treatment of oil wastewater. By the effect of a certain driving force, water penetrates the membrane, while oil is blocked outside the membrane, thus achieving the purpose of oil-water separation (CN103601826A, and Industrial & Engineering Chemistry Research (2014, Volume 53, Page 6401-6408, Surface hydrophilicity of hydrophilic modified polyvinylidene fluoride membrane prepared by non-solvent phase conversion, and effects thereof on oil/water separation)). It has a water flux of 90 L/(m2·h·bar) in the treatment of kerosene-water mixture, but shows high processing cost, poor oil pollution resistance, and the membrane pores are easily blocked. In the case of treating oily wastewater with relatively few oil contents, the hydrophilic-oleophobic membranes must afford high water pressure to drive water to penetrate, thus requiring large membrane areas and high energy consumption. For treating the same oily wastewater of the hydrophobic-oleophilic membranes, through oil and intercept water may be more economical. However, the hydrophobic-oleophilic membranes reported have some drawbacks including high preparing cost, complicated process, difficult to large-scale production, consistently reduced hydrophobicity and low mechanical strength.